1. Field of the Invention
This invention relates to a motor drive unit for accommodating electrical components used in controlling an AC motor.
2. Description of the Related Art
A motor drive circuit shown in the circuit diagram of FIG. 4, by way of example, is used as a control apparatus for an AC motor which drives the spindle or feed shaft of a machine tool. Electrical components such as an electromagnetic contactor A, rectifying diode B, smoothing capacitor C, regenerative transistor D, transistor bridge E and filter F, as well as electrical components such as a power resistor and fuse, are connected to a circuit extending from three-phase AC power supply terminals R, S, T shown in FIG. 4 to terminals U, V, W for feeding current to the AC motor.
The large electrical components among these components are connected to a mounting board by screws and are connected by using a cluster of wires, after which the components are housed in a metal case consisting of worked sheet metal.
In the control apparatus accommodated in the abovementioned metal case, the various electrical components which are each of a different shape are first fixed and then interconnected by the cluster of wires. Consequently, assembling the motor drive unit requires labor, and thus, automating the operation as by using an assembling robot involves many difficulties.
Furthermore, since the worked sheet-metal case is used as the external housing, problems arise in terms of cost and weight.